Latest update:
I ordered the parts for AWH-059, including the diodes I originally wasn't going to order. (side note: I actually ordered both types; 1n4004 and 625-srp300g-e3)
Removed and replaced:
C1, C2, C3, C4, C5, C6, C11, C12.
Q1, Q2, Q3, Q4,<--those were done previously Q5, Q6, Q7, Q8, Q9, Q10, Q11, Q12
R20
VR1, VR2, VR3, VR4
With everything replaced, I made an executive decision to put it all back together. First, I reconnected the cut wires 2 and 3 on the power supply board. Then I went back to AWH-059 and replaced D8 and D10 with the srp300g-e3's, then cleaned the old thermal paste from the output transistors and mica shields, applied new paste (non-conductive Ceramique 2) and reinstalled those. Lastly I resoldered the leads to STV-4h diode.
I placed the large heatsink back into position, and made sure the board was set so that no metal was being contacted. (I chose to leave the full metal shield that goes behind the board off in case further work was needed)
Then I built a DBT, plugged it into the wall, and plugged the 850 into the DBT.
I gave the board one more visual once-over, took a deep breath...and flicked the switch on the DBT.
The bulb glowed brightly, then dimmed. Nice! The relay didn't click, but to tell the truth, I don't know if it's supposed to with the DBT or not. The fact that it glowed brightly, then dimmed, was enough of a success for me.
I knew I wasn't out of the woods yet. I still had to adjust VR1, 2, 3, 4. Having never done the procedure, I was fairly certain they could not be properly adjusted while still plugged into the DBT. (post note: my previous searches for tickling the dragon turned up only the DBT and running the unit on low power for a while. I now discovered the trim pots
can be adjusted while using the DBT to determine if the unit will power up safely)
I unplugged my 850 from the DBT, and plugged it into house current.
Making sure the volume was down and no speaker buttons depressed, I took a bigger breath, and flicked the power switch...
After a couple of seconds, the metallic click of the relay instantly became the sweetest sound in the world. I rested my head against the faceplate, just so thankful.
However, would the trim posts adjust to spec? The answer was yes. I was able to get VR1 and VR2 to near perfect (0.000 to 0.001) and VR3 and VR4 to 20mv.
I let the unit warm up for 10-15 minutes, and rechecked the trim pots. Just a tiny tweak was all that was required for VR1, VR2 and VR3, and VR4 was still spot on.
I then connected speakers, dialed in an FM station, and gave a little volume. Music flowed out of my JBL L-50's. I was grinning like a little kid.
I then shut it all down, and put everything back together. I hooked my receiver back into the lineup (an RG-2, SG-9500 equalizer, and RT-707 r-t-r) loaded up a tape, and hit play.
Yeah, big ol' kid grin. Again.
It's been a long couple of months, and I want to thank all that offered help, insight and thoughts. And a special thanks to Mark for his willingness to help track down what was going on. (I
think, despite a good ohm reading, that R20 was the culprit?)
I ran the tape for a couple of hours last night on low volume, and am playing the other side as I type this. I haven't yet tried any significant volume.
I do have one question: I can't remember if it's normal for the function lamp to go brighter when turning OFF the speaker button? It doesn't matter which function button is depressed, each one gets brighter when the speaker button goes off. The only one unaffected is the Stereo lamp for FM. Its illumination stays constant. Oh, switching speaker inputs yields the same results, so plugging into Speaker B doesn't change the symptom (if it is one!)
If someone thinks there is a problem, I will start a new thread.